This invention relates to hybrid organic-inorganic conjugated polymers for preferred applications in opto-electronic devices, such as electroluminescent displays, solar cells, sensor, thin film organic transistors, lasers and electrochemical cells. Also provided is a process for making the conjugated polymers of the present invention.
In a surprising departure from the prior art, the inorganic portion of the hybrid conjugated polymers of the present invention contain segments of silsesquioxane in the polymer backbone or as pendant groups.
It is known that polymers with conjugated backbone such as poly(p-phenylene), poly(p-phenylenevinylene), polyfluorene, polythiophene and polyaniline are important class of materials for applications in electronic and optical devices. However, these polymers are difficult to process and fabricate into devices due to their poor adhesion, low solubility and instability at high temperature.
U.S. Pat. No. 5,247,190 discloses an electroluminescent device comprising a light emitting layer derived from a thin film of poly(p-phenylenevinylene) wherein the phenylene ring may optionally carry one or more substituents each independently selected from alkyl, alkoxy, halogen or nitro groups.
U.S. Pat. No. 5,869,350 teaches to fabricate electroluminescent devices using solvent soluble light emitting polymers such as poly(2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene).
PCT Patent Application WO 98/27136 teaches to prepare soluble aryl substituted poly(p-phenylenevinylene) for applications in electroluminescent devices. The co-polymerization of different aryl substituted monomers produced polymers that emit light at different wavelengths.
U.S. Pat. No. 5,817,430 teaches to prepare substituted derivatives of poly(p-phenylenevinylene) for applications in electroluminescent devices by using organic chain end controlling additives to improve the solubility.
Although the use of organic conjugated polymers have been substantial promise for electrooptical applications, devices made from these materials are still suffering from short useful lifetime. The lifetime of such devices and the stability of materials under operation conditions remain important issues for commercialization.
One cause responsible for device instability was shown to be polymer interchain interactions such as aggregation, excimer formation, and polaron pair formation.
Hence, controlling interchain interactions remains a challenge in the design and synthesis of such conjugated polymers. Otherwise various electrooptical applications would not be possible under normal operation.
One potential approach at solving this problem has been the introduction of structural asymmetry in the polymer chain thereby limiting its ability to pack effectively in the solid state. For example, Son et al [Son, S., etal., Science, 1995, 269, 376] engineered the distribution of cis-linkages in poly(phenylenevinylene) chains. The cis linkages interrupt conjugation and interfere with the packing order of the polymer chains. Pang et al. [Liao, L., Pang, Y., et al., Macromolecules, 2001, 34, 7300] introduced a meta-linkage in the main conjugated chain of the polymer and the meta-linkage simultaneously interrupts the conjugation length of a π-conjugated polymer and allows the polymer to bend and twist more effectively than a para-linkage.
Another potential approach has been to design a polymer that is structurally required to twist in a manner that limits or precludes effectively π-stacking, while still having sufficiently long conjugation length chromophores to allow fine-tuning of the emission wavelength, intensity and lifetime.
However, one approach remains unexplored. Thus the present invention relates to a third approach relying on the use of bulky and structural substituents to limit close approach between aromatic chromophores. This approach is surprisingly advantageous in many respects. By having selected effective bulky substituents, the present inventors have been able to provide conjugated polymers having reduced chain mobility and reduced interchain aggregation. The polymers of the present invention display a preventative effect on excimer formation and an increase in thermal stability. The improved properties will provide an increase in the efficiency and lifetime of devices made from these polymers. The preferred bulky substituents are from a known genus of compounds called silesquioxanes.
In a parallel and somewhat unrelated art, it is known that hybrid organic-inorganic polymers containing segments of silsesquioxane exhibit a number of potentially useful properties including high temperature stability in air and good adhesion to a number of substrates. These materials are also resistant to oxidation and degradation by ultraviolet light. They have been used as protective coatings for electronic devices and other substrates and as precursors for ceramic coatings, foams, fibers, and other articles.
However, it has not been known in the art to use silsesquioxane segments in the design and preparation of conjugated polymers having opto-electronic properties such as light emitting polymers.
For example, U.S. Pat. No. 5,484,867 teaches the preparation of reactive polyhedral oligomeric silsesquioxane oligomers and to the subsequent synthesis of polymers containing the resulted segments of silsesquioxane. However, such polymers do not emit light nor exhibit any opto-electronic properties.
U.S. Pat. No. 5,589,562 teaches the preparation of linear copolymers, which contain regularly alternating segments and bridging group segments of silsesquioxane. Again, such polymers do not emit light nor exhibit opto-electronic properties.
Thus, the prior art, in general has failed to provide conjugated polymers combining excellent opto-electronic properties and advantageous stability under normal operating conditions of opto-electronic devices.
It is thus an object of the present invention to remedy the disadvantages of the prior art by providing hybrid organic-inorganic conjugated polymers having improved stability rendering these polymers useful and stable under normal operating conditions of opto-electronic devices.